Both are needed to know which stroke each piston is in
Variable valve timing or not, on four-stroke engines the camshaft spins at half the speed of the crankshaft.
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This means that for any given crankshaft angle there are two possible camshaft positions, which means that knowing the crank angle alone is not enough to eliminate aliasing, therefore not enough to know when to ignite the spark plug/fire the injector.
It is therefore mandatory in distributor-less setups to have input from both sensors to determine which stroke each piston is in.
